With the widespread dissemination of cameras, technology for taking three-dimensional (3D) images using information about a distance to an object as well as a two-dimensional image of the object has received attention. A device for acquiring information about a distance to an object and sensing the distance is called a depth sensor. A 3D image sensor that obtains a 3D image using the depth sensor is called a 3D image sensor.
The depth sensor measures a delay time between pulse light emitted from a light source which is then reflected from an object and received by the image sensor. A pixel of the depth sensor includes a plurality of photoelectric conversion elements. Each of the photoelectric conversion elements generates photocharge in proportion to the quantity of pulse light emitted by a light source and then reflected and returned from the object. A difference between a time of emission of the pulse light and a time of sensing the pulse light is called a time of flight (TOF). The distance to the object can be calculated from the TOF and the speed of the pulse light. In other words, the depth sensor calculates the distance to the object using the charge generated by the photoelectric conversion element. A 3D image can be realized using the distance calculated by the depth sensor and color information acquired by another sensor. However, the quality of the 3D image may be low due to various types of interference. Techniques for preventing the interference have been developed.